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In the more common non artesian or watertable condition, aquifer discharge is
passive, driven by evaporation and soil water content. Nulsen ( 1981 ) described the
capacity of groundwater to be evaporated from the capillary fringe as a function of
depth to the watertable, soil material, and potential evaporation rates and indicated
it was unlikely for sufficient salt transport to take place and impact the yield of
wheat and barley at watertable depths of greater than 1.5 to 1.8 m. This was con-
firmed by a study by Bennett et al. ( 2012 ) who showed that passive salt flux and
saline runoff was reduced on a broad and saline valley when the link between the
capillary fringe and soil surface was reduced by lowering the watertable.
4.4.2 Classification Based on Groundwater Discharge Type
To enable managers to define the source and options for salinity management,
George et al. ( 1997 ) defined ten common hydrogeological settings for salinisation
in the WA context. This system was modified by Coram et al. ( 2000 ) and then
increased to 15 hydrogeological settings for the Australian context (NLWRA 2001 ).
These geologic and geomorphic based conceptualisation of flow systems responsi-
ble for salinity (with the flow systems classification defined above) enabled manag-
ers to select the most likely options and assist to define the areas for treatment
(Clarke et al. 2002 ).
Some common examples of dryland salinity seeps are shown in Fig. 1. Anything
that causes groundwater flows to approach the soil surface will result in a seepage
point. The examples are two dimensional but they may be water converging on a
point in the landscape from multiple slopes, or changes in the hydraulic conductiv-
ity of the regolith as occurs over dolerite dykes (Engel et al. 1987 ). This investiga-
tion also was one of the first applications of electromagnetic and magnetometer
instruments to understanding dryland salinity problems.
4.5 Comparison of Dryland and Irrigation Salinity
As indicated in a previous section, irrigation salinity affects about twice the land
area and has a tenfold higher incidence on a percentage area basis. While there are
many common characteristics, it differs from dryland salinity in several important
aspects:
(i) Irrigation water is often a major source of the salt;
(ii) Irrigation water can also be a major contributor to high groundwater levels
which brings soluble salts to the surface and results in concentration by both
transpiration and soil evaporation;
D.J. McFarlane et al.